Sharper than Hubble: Large Binocular Telescope achieves major breakthrough

A picture of the movable secondary mirror during its installation in the Arcetri lab. The image shows the 672 tiny magnets spread over the back of the mirror. The reflecting face of the mirror is face down. The upper portion contains the electro-mechanical devices that control the magnets. Image: LBT Collaboration / R. Cerisola

(PhysOrg.com) -- The next generation of adaptive optics has arrived at the Large Binocular Telescope (LBT) in Arizona, providing astronomers with a new level of image sharpness never before seen. Developed in a collaboration between Italy’s Arcetri Observatory of the Istituto Nazionale di Astrofisica (INAF) and the University of Arizona’s Steward Observatory, this technology represents a remarkable step forward for astronomy.

The LBT, with its two 8.4 metre -mirrors, is the largest single optical telescope in the world. The telescope is a collaboration between institutions from the USA, Italy and Germany. Germany’s 25% participation is represented by the Max-Planck Society, the Astrophysical Institute Potsdam and Heidelberg University. The test camera for the images shown here was developed by INAF and the Max-Planck-Institute for Astronomy (MPIA) in Heidelberg.

Until relatively recently, ground-based telescopes had to live with wavefront distortion caused by the Earth’s atmosphere which significantly blurred images of distant objects (this is why stars appear to twinkle to the human eye). While there have been advancements in adaptive optics technology to correct atmospheric blurring, the LBT’s innovative system truly takes this concept to a whole new level.

In closed-dome tests beginning May 12 and sky tests every night since May 25, astronomer Simone Esposito and his INAF team tested the new device, achieving exceptional results. The LBT’s adaptive optics system, called the First Light Adaptive Optics system (FLAO), immediately outperformed all other comparable systems, delivering an image quality greater than three times sharper than the Hubble Space Telescope using just one of the LBT’s two 8.4 metre mirrors. As soon as the adaptive optics are in place for both mirrors and their light is combined appropriately, it is expected that the LBT will achieve image sharpness ten times that of the Hubble.

"This is an incredibly exciting time as this new adaptive optics system allows us to achieve our potential as the world’s most powerful optical telescope," said Richard Green, director of the LBT. "The successful results show that the next generation of astronomy has arrived, while providing a glimpse of the awesome potential the LBT will be capable of for years to come."

The unit of measure for perfection of image quality is known as the Strehl ratio, with a ratio of 100 % equivalent to an absolutely perfect image. Without adaptive optics, the ratio for ground-based telescopes is less than 1 percent. The adaptive optics systems on other major telescopes today improve image quality up to about 30 percent to 50 percent in the near-infrared wavelengths where the testing was conducted.

A double star as observed with the LBT in standard mode (left), and with the adaptive correction activated (right). Because of atmospheric blurring, the fainter companion of the star cannot be identified in the images taken in standard mode, while it is easily visible when the adaptive module is activated. A third faint star also becomes visible in the upper right part of the frame, thanks to the increased sensitivity of the telescope in adaptive mode. Image: LBT Collaboration

In the initial testing phase, the LBT’s adaptive optics system has been able to achieve unprecedented Strehl Ratios of 60 to 80 percent, a nearly two-thirds improvement in image sharpness over other existing systems. The results exceeded all expectations and were so precise that the testing team had difficulty believing their findings. However, testing has continued since the system was first put on the sky on May 25, the LBT’s adaptive optics have functioned flawlessly and have achieved peak Strehl ratios of 82 to 84 percent.

"The results on the first night were so extraordinary that we thought it might be a fluke, but every night since then the adaptive optics have continued to exceed all expectations. These results were achieved using only one of LBT’s mirrors. Imagine the potential when we have adaptive optics on both of LBT’s giant eyes." said Simone Esposito, leader of the INAF testing team.

Development of the LBT’s adaptive optics system took more than a decade through an international collaboration. INAF, in particular the Arcetri Observatory, conceived the LBT instrument design and developed the electro-mechanical system, while the University of Arizona Mirror Lab created the optical elements, and the Italian companies Microgate and ADS International engineered several components. A prototype system was previously installed on the Multiple Mirror Telescope (MMT) at Mt. Hopkins, Arizona. The MMT system uses roughly half the number of actuators as the LBT’s final version, but demonstrated the viability of the design. The LBT’s infrared test camera, which produced the accompanying images, was a joint development of INAF, Bologna and the MPIA, Heidelberg.

"This has been a tremendous success for INAF and all of the partners in the LBT," said Piero Salinari, Research Director at the Arcetri Observatory, INAF. "After more than a decade and with so much care and effort having gone into this project, it is really rewarding to see it succeed so astoundingly."

This outstanding success was achieved through the combination of several innovative technologies. The first is the secondary mirror, which was designed from the start to be a main component of the LBT rather than an additional element as on other telescopes. The concave secondary mirror is 0.91 metres in diameter (3 feet) and only 1.6 millimetres thick. The mirror is so thin and pliable that it can easily be manipulated by actuators pushing on 672 tiny magnets glued to the back of the mirror, a configuration which offers far greater flexibility and accuracy than previous systems on other telescopes. An innovative "pyramid" sensor detects atmospheric distortions and manipulates the mirror in real time to cancel out the blurring, allowing the telescope to literally see as clearly as if there were no atmosphere. Incredibly, the mirror is capable of making adjustments every one thousandth of a second, with accuracy to better than ten nanometres (a nanometre is one millionth the size of a millimetre).

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Sharper than Hubble: Large Binocular Telescope achieves major breakthrough (2010, June 15)
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Well written with enough technical information to meet a high level of interest. Also nice to see relevant pictures. The star picture demonstrates what the technology can actually do. Thank you for not using an "artist's concept".

This is very good news indeed. By the time the Hubble is taken out of service, ground based instruments will be able to create images as sharp or even more sharp than the Hubble ever could produce. I expect great discoveries as a result of this technology.

Does this mean space based telescopes will become less important since we've solved the atmosphere problem and land based telescopes can be made much larger and cheaper?

Depends. If we find a cheap way to get stuff to orbit then large orbit based telescopes may be competitive. Compensating atmosphere does not mean reducing atmospheric influence to zero (there is always _some_ absorption/scattering effect - even in compensated pictures)

Then there are all the telescopes which work at frequencies which are blocked a lot by the atmosphere (e.g. X-ray/far gamma telescopes). In that case space based telescopes will probably keep outperforming ground based ones

@Donkersair disturbance is a non linear system - you can make models very close to approximate it but in the end all models of non linear systems aren't very good...

Well well, at last some truth!So... just changing the subject slightly, does that mean that the IPCC models used to predict the climate 100 years into the future are actually linear? No, right?Sooo.... what?

I agree that adaptive optics can cancel out the lensing effect of the miles of atmosphere between the source and eyepiece however there are a lot of weaker rays of light that never even reach our telescopes due to atmospheric dispersion. This is significant amount of lost information (which an orbital system like Hubble could capture to some extent). For e.g. imagine trying to capture the deep field with LBT. Just in case this was used in a orbital platform, I wish the LBT's adaptive algorithms can be programmed to counter other aspects of distortion that exist while making observations in a vacuum.

"1. Hubble is set up to detect infrared as well as visible light. Infrared is absorbed by atmosphere.2. Hubble can monitor day and night without being blocked by Earth."

Also, Hubble could get ultraviolet, which doesn't penetrate the atmosphere well. Many overlook the largest shortcoming of Hubble. It can operate only about 20 minutes of each 90 minute orbit. The rest of its life is spent getting into protective mode before exposure to the sun or getting out of that mode and stabilizing internal temperature before it can be used again.

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